ASSESSMENT OF PROPERTIES OF TRANSIENT LIQUID PHASE SINTERED (TLPS) INTERCONNECTS BY SIMULATION AND EXPERIMENTS
Greve, Hannes Martin Hinrich
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Growing power densities of electronic products and application of electronic systems in high temperature environment increase the temperature requirements on electronic packaging systems. Conventional interconnect technology was designed for devices based on silicon semiconductor technology limited to 175 °C and below. The introduction of wide bandgap semiconductor materials such as silicon carbide and gallium nitride expands the potential application temperature range to 500 °C beyond the range of conventional electronic packaging solutions. Transient Liquid Phase Sintering (TLPS) is a promising high temperature, high strength, low cost interconnect technology solution. TLPS is a liquid-assisted sintering process during which a low melting temperature constituent melts, surrounds, and diffuses with a high melting temperature constituent. A shift towards higher melting temperatures occurs as the low melting temperature phase is transformed into high melting temperature intermetallic compounds (IMCs). In this work, three TLPS sinter paste systems based on the copper-tin (Cu-Sn), nickel-tin (Ni-Sn), and copper-nickel-tin (Cu-Ni-Sn) material systems are designed. A novel process for their application as electronic interconnects is developed. Processing and thermal aging studies are performed to determine times to process completion characterized by high-temperature capability of the joints. Microstructural convergence durations are studied for each of the material systems. A modeling approach is developed to model realistic joint geometries with varying types, sizes, and distributions of metal particles and voids in intermetallic matrices. These are used to predict the constitutive (elastic-plastic) stress-strain responses and thermal properties of these systems by simulation. The constitutive models derived by this approach are compared to constitutive properties determined experimentally by Iosipescu shear samples with TLPS joints. The thermal properties of TLPS joints are determined experimentally by transient thermal response analyses. Failure mechanisms driven by thermal and thermo-mechanical stressors are predicted and verified, and mitigation techniques are developed.